docs: def execute(self, using=None):
          """
          Populate the database using all the Entity classes previously added.
  
          :param using A Django database connection name
          :rtype: A list of the inserted PKs
          """
          if not using:
              using = self.getConnection()
  
          insertedEntities = {}
          for klass in self.orders:
              number = self.quantities[klass]
              if klass not in insertedEntities:
                  insertedEntities[klass] = []
              for i in range(0,number):
                      insertedEntities[klass].append( self.entities[klass].execute(using, insertedEntities) )
  
          return insertedEntities